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Global Warming Shrinks the Fish: Salmon off the Menu by 2050?

Update Date: Oct 01, 2012 12:20 PM EDT

Here is a controversial statement yet to be uttered this election year---Global warming is a fact!  

Polar ice caps are melting at an accelerated rate, ocean levels are rising and low lying islands and coastlines on our planet are becoming submerged forever. These are scientific facts and are non debatable occurences that will continue unless global actions are taken to slowdown the process.Scientists have conducted research on the impact on 600 species of ocean dwellers of rising water temperatures in the world's oceans between 2001 and 2050.  

 Relatively small increases in water temperature will significantly affect fish sizes by decreasing their size by up to 24% by 2050. Fish body size is related to water temperature and oxygen level. Warmer waters could decrease ocean oxygen levels and significantly reduce fish body weight.The model built by the Intergovernmental Panel on Climate Change (IPCC), tested how fish would react to lower levels of oxygen in the water.

Although this data projects relatively small changes in temperatures at the bottom of the oceans, the resulting impacts on fish body size are "unexpectedly large" according to the paper. As ocean temperatures increase, so do the body temperatures of fish.

But, according to lead author, Dr. William Cheung, from the University of British Columbia, the level of oxygen in the water is key. "Rising temperatures directly increase the metabolic rate of the fish's body function," he told BBC News. "This leads to an increase in oxygen demand for normal body activities. So the fish will run out of oxygen for growth at a smaller body size. So in, say, the North Sea," says Dr. Cheung, "one would expect to see more smaller-body fish from tropical waters in the future."

The largest decreases I fish sizes are expected in the Indian and Atlantic oceans. When compared with actual observations of fish sizes, the model seems to underestimate what's actually happening in the seas. The researchers looked at two case studies involving North Atlantic cod and haddock. They found that recorded data on these fish showed greater decreases in body size than the models had predicted. Other scientists say the impact could be widely felt. 

Dr. Alan Baudron, from the University of Aberdeen, UK, has studied changes in the growth of haddock in the North Sea. He says this latest research is a "strong result". He believes it could have negative implications for the yields of fisheries.

And it could also seriously impact the ability of fish to reproduce, he adds.In an interview with BBC News, Dr. Baudron said, "Smaller individuals produce fewer and smaller eggs which could affect the reproductive potential of fish stocks and could potentially reduce their resilience to other factors such as fishing pressure and pollution.

The scientist point out a number of limiting factors in their study, including uncertainties in the predictions for the climate and the oceans. According to Dr. Cheung, further research is required. "Our study shows that climate change can lead to a substantial decrease in the maximum body weight of fish. We need to look more closely at the biological response in the future."Smaller fish, fewer numbers of fish and overfishing will mean that we will deplete our oceans for future generations.    

 The research was published in the journal Nature Climate Change. 

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